Bituminous coal liquefaction process

ABSTRACT

Economical and efficient carbonaceous material liquefaction is achieved to provide high yields of aralkanes for liquid fuels. Comminuted carbonaceous material as an aqueous slurry is combined with supercritical water at temperatures and pressures to provide thermal cracking of alkane bonds in the presence of hydrogen. This process converts the carbonaceous material to liquids, primarily aralkanes, gaseous hydrocarbons and undissolved ash. The supercritical effluent is then separated into a product fluid stream and a solid fraction. The pressure of the fluid phase is reduced, resulting in formation of a gaseous fraction comprised mainly of hydrogen, water vapor and low molecular weight gaseous hydrocarbons, and a liquid fraction, which separates into an organic phase and an aqueous phase. The organic phase which is rich in aralkanes is then scrubbed to remove any acidic or basic constituents and is processed in accordance with conventional techniques. The aqueous phase may be recycled after impurity rejection.

United States Patent 1191' Stewart, Jr. et al.

1451 Nov. 26, 1974 BITUMINOUS COAL LIQUEFACTION 3,755,136 8/1973 Fieldset al. 208/8 E S 3,775,071 11/1973 Hoffertet al... 208/8 PROC S3,808,119 4/1974 Bull et al. 208/10 [75] Inventors: A. Theodore Stewart,Jr., Woodside;

Dyer San Rafael both of Primary Examiner-Delbert E. Gantz Cahf-Assistant Examiner-Veronica OKeefe [73] Assignee: Bechtel InternationalCorporation, Y Agent, Firm-Townsend and Townsend San Francisco, Calif.1221 Filed: Dec. 6, 1973 [57] {*BSTRACT Economlcal and eft'lclentcarbonaceous materlal llque- PP 422,497 faction is achieved to providehigh yields of aralkanes for liquid fuels. Comminuted carbonaceousmaterial [52] us. c1. 208/8 as an aqueous Slurry is Combined withsupercrhha' [51] Int. Cl C10g l/06 Water at temperatures and pressuresto provide [58] Field 61 Search 208/8 cracking of a'kahe hhds thePresence f drogen. This process converts the carbonaceous mate- 56 R f dI ml to liquids, prlmarlly aralkanes, gaseous hydrocar- UNITE]; gl lizfZZ bons and undissolved ash. The supercritical effluent is thenseparated into a product fluid stream and a solid .lannek et al fractionThe pressure f the phase is reduced gf 2 1 resulting in formation of agaseous fraction comprised 5x936 8 5 8 mainly of hydrogen, water vaporand low molecular 7/1936 Lowry Jr 208/8 weight gaseous hydrocarbons, anda liquid fraction, 2:871:18] 1/1959 Kulik ....,:::I::::.... I: 208/8which separates into an Organic Plhase and an aqueous 3.109.803 11/1963Bloomer et a]. 208/8 P The Organic Phase WhiCh is rich in aralkanes is3,240,566 3/1966 Bullough et al 208/8 then scrubbed to remove any acidicor basic constitu- 3.375,188 3/1968 Bloomer 208/8 ents and is processedin accordance with conventional 3,453,206 7/1969 Gatsis 208/210techniques. The aqueous phase may be recycled after t e au ey 3.694.3429/1972 Sprow et =11 208/ 5 C m 1 awing igur SCRUBBER 24 CONZSSSER LIQUIDHEAT 1 SEPARATOR IO EXCHANGER 34 1, I4 SOLIDS 36 REACTOR SEPARATOR 1BITUMINOUS COAL LIQUEFACTION PROCESS BACKGROUND OF THE INVENTION 1.Field of the Invention The ever increasing requirements for liquid fuelsand the uncertainties of supply from the major known proven oil reserveshave accelerated interest in alternative sources for liquid fuels. Onesource which has received extensive study over a long number of years iscoal, particularly bituminous and subbituminous coal. Coal is comprisedof a substantial amount of high molecular weight hydrocarbon,particularly polymers having arylene and alkylene links, which can serveas a source of liquid fuels by cracking under reducing conditions.

Coking of coal produces about 1 percent by weight of light oils, whichare primarily aromatic hydrocarbons. A large amount of the hydrocarboncontent of the coal is converted to char and highly aromatic solidhydrocarbons. In order to enhance the yield of the light oil fractions,numerous processes have been proposed.

Upon pyrolysis of the hydrocarbons in the solid coal phase, there isample opportunity for the resultant free radicals or other high energyproducts of the pyrolysis to react with each other and form asphaltenes,we well as other high molecular weight materials. To minimize asphalteneformation, it is desirable. to both maintain the hydrocarbon fraction ofthe coal relatively fluid and esily mobile, and to provide a sufficientamount ofa hy-' drogen source, so that the hydrogen will react with thehighly reactive pyrolytic fractions, so as to prevent them fromrecombining into high molecular weight products.

In processing the coal, it is desirable to use inexpensive agents whichdo not require recovery or can be easily or inexpensively recovered inreusable form. Furthermore, the materials employed should allow easyseparation of the ash and undissolved components, should be easilyseparable from the desired liquid product and should not interfere withthe formation of the liquid fuel fraction. Since catalytic systemsfrequently require pretreatment of the coal, as well as recovery andrejuvenation of the catalyst, a preferred system should not require acatalyst.

2. Description of the Prior Art US Pat. Nos. 1,695,914; 1,936,819;2,012,318 and 2,041,858 employ water, coal and a reducing metal, i.e.iron or zinc in processing comminuted coal to provide liquidcarbonaceous materials. US. Pat. Nos. 1,931,550 and 3,488,280 teachcatalytic hydrogenation of coal in the presence of water. U.S. Pat. No.3,660,269 teaches employing a small amount of water with coal, ahydrocarbon solvent and hydrogen in a fluidized bed to reduce asphalteneformation. U.S. Pat. No. 3,453,206 treats oils with water and hydrogenat elevated temperatures and pressures to reduce sulfur and asphaltenecontent.

SUMMARY OF THE INVENTION Economic and efficient production of liquidfuel fractions from carbonaceous materials, particularly coal, isprovided. Using coal as illustrative, comminuted coal as an aqueousslurry is contacted with supercritical water at temperatures andpressures to provide thermal cracking of alkane bonds in the presence ofhydrogen. The method of contacting the coal with the water minimizes thetime required to raise the coal to the desired cracking temperature. Theprocess converts the coal to liquids, primarily aralkanes, gaseoushydrocarbons and undissolved ash. The supercritical effluent isseparated into a product fluid stream and a solid fraction which may becombusted to provide heat for the process. The pressure of the fluidphase is then reduced to allow for the formation of a gaseous fractioncomprised mainly of hydrogen, low molecular weight gaseous hydrocarbonsand water vapor and a liquid fraction containing hydrocarbons and water.The organic phase is separated from the aqueous phase. After theseparation, the organic phase may be scrubbed free of acidic andbasicmaterials and processed according to conventional techniques. Theaqueous phase may be recycled after provision is made for impurityrejection.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a flow sheet diagram of amethod according to this invention.

BRIEF DESCRIPTION OF THE SPECIFIC EMBODIMENTS The effluent from thereactor is then transferred to a solids separation zone and separatedinto a fluid phase and a solid phase. The solid phase containing ash andundissolved organic material may be combusted for process heat. Thepressure of the fluid phase is transferred to a subsequent zone in whichthe temperature and pressure are reduced in one or more stages. Thecondensation occurs in heat exchanging relationship with water, which isthen employed in the reactor after being brought to the desiredtemperature and pressure. Gaseous products are taken overhead and theunreacted hydrogen may be recovered and reused. The liquid phase istransferred to a separation zone and separated intotwo phases, anaqueous phase and an organic phase. The organic phase may then bescrubbed free of acidic and basic. materials and processed according toconventional techniques. Various naturally occurring carbonaceousmaterials may be employed as a source of the carbonaceous material.Coal, other than anthracite, such as bituminous or subbituminous coalmay be employed. In addition, lignite, peat, shale, and the like mayalso be used.

The carbonaceous material will be employed as an aqueous slurry. Thecarbonaceous material will be comminuted to particles in the size rangeof from about 200 Tyler mesh to about A: inch, more usually from aboutTyler mesh to about V4 inch, and preferably in the range of about 200 to100 Tyler mesh.

The comminuted carbonaceous material will then be slurried with water,so as to provide a. conveniently mobile stream. The amount of wateremployed should be the minimum required to provide a convenientlyflowable slurry. Normally, the water will be less than about one-half,frequently equal to or less than about onethird the total amount ofwater introduced into the reactor. Usually, the amount of water in theslurry will be from about 0.25 to about 0.75 parts by weight per part ofcoal, more usually from about 0.4 to 0.6 parts by weight per part ofcoal. The less water employed in the slurry, the lower the temperaturerequirement for the supercritical water introduced into the reactor.

The carbonaceous material which is employed need not be treated toremove ash or moisture. In this way, processing of the coal or othercarbonaceous material prior to introduction into the reactor isminimized.

In the reaction zone the process may be carried out as a batch processor a continuous process, but is preferably carried out as a continuousprocess.

While many different carbonaceous materials may be used, coal ispreferred and will be employed as illustrative.

Concomitant with the introduction of the coal slurry, water undersupercritical conditions and hydrogen are introduced into the reactionzone. The primary source of heat for the reaction is introduced byheating the feed water, elevating it to supercritical conditions.Additional heat is added in the reaction zone as a result of theexothermic nature of the reaction. The temperature of the heated waterwill be sufficient to bring the reaction medium to a temperature of atleast 380C, and not greater than about 650C, more usually in the rangeof about 400500C. The total amount of water, including the wateremployed in providing the slurry, will be at least about 0.5 parts byweight per part of coal and not exceed about parts by weight per part ofcoal. Usually, the total amount of water will be in the range of about1-5 parts by weight per part of coal and preferably from about 1 to 2parts by weight per part of coal.

Hydrogen can be employed by itself, or as a mixture with water andcarbon monoxide as obtained with water gas, synthesis gas, and the like.The amount of water present with the hydrogen is included in the totalamount of water employed. Other gases may also be present which do notinterfere with the reaction. The hydrogen can be introduced as aseparate stream or can be mixed with the supercritical water, so thatonly two streams are simultaneously metered into the reaction zone. Theamount of hydrogen employed will be at least about 0.5 weight percentbased on coal and not exceed about weight percent based on coal, moreusually being from about 1 to 10 weight percent based on coal andpreferably from about i to 4 weight percent based on coal.

The contact time in the reaction zone will generally be at least oneminute and not exceed about 10 minutes, more usually being in the rangeof about i to 5 minutes. The particular contact time will vary with thetemperature employed, the carbonaceous material, the ratio of reactants,and the like. The time required to bring the coal to reactiontemperature will be less than about 0.5 min.

The pressure in the reactor will be at least about 3,300 psi (about 230atm.) and generally not exceed 10,000 psi (about 700 atm.) preferablybeing in the range from about 3,500 psi (about 245 atm.) and notexceeding about 5,000 psi (about 350 atm.). By maintaining highpressures, a dense compact reaction medium is employed which insuresefficient extraction from the coal of the desired hydrocarbons,minimizing side reactions to undesirable products.

The streams entering the reaction zone are brought together so as toprovide agitation and effective contact of the coal with the gases. Bynot heating the coal slurry significantly prior to its rapid contact inthe reactor with water at supercritical temperatures, the coal israpidly brought up to pyrolytic temperatures without significantresidence time at temperatures below the reaction temperature.

While still at a supercritical temperature, the reaction mixture istransferred to a solids separation zone to separate the fluid streamfrom the solids. The solids may be separated by filtration,centrifugation, sedimentation, or other convenient means, and recoveredto be used as a fuel, a source of hydrogen, or otherwise processedaccording to known procedures. Because of the high efficiency of theconversion to liquid fractions, the amount of solids will only be asmall proportion of the total solids charged.

The fluid stream is flashed into a condensing and heat exchanging zonewere gaseous products, mainly hydrogen and small amounts of gaseoushydrocarbons, e.g. methane, are carried overhead, while the organic andaqueous phases are cooled to below their boiling points C.) at ambientpressures.

The condensing and heat exchanging zone may be comprised of one or morestages and may be separate or combined for the gaseous and liquid phasecooling. The first stage can provide heat exchange with the vapors underthe exit conditions of temperature and pressure from the solidsseparation zone. A second stage can provide adiabatic and condensationexpansion of the vapors.

The gaseous effluent may be processed to remove any undesirable reactiveminor constituents, such as hydrogen sulphide, and then recycled to thereaction zone. The hydrogen can be separated from gaseous hydrocarbons,and acidic gases prior to introduction into the reaction zone.

in order to conserve energy, the water stream which is to be fed to thereaction zone is heated by indirect heat exchange with the vapor phasein the coolingcondensing zone, providing the necessary cooling of thevapor phase, while absorbing the heat from the vapor phase. in thismanner, once the process has been initiated, only minor amounts ofsupplemental heat is required to maintain the reaction mixture at thereaction temperature. This supplemental heat can be derived from the useof the solids from the separation zone as a fuel.

The combined liquid phases are now transferred to a separation zone,where the aqueous phase is separated from the organic phase.Centrifugation, chemical demulsifiers, ultrasonic treatment or the likemay be employed. Any emulsification which results can be rapidly brokenby mechanical or physical means.

The aqueous phase will contain a major portion of low molecular weightsulfur and nitrogen containing compounds, such as any hydrogen sulphideand low molecular weight amines. The water may be processed for reuse.The organic phase, after separation from the aqueous phase, may befurther processed by percolating through one or more scrubbers havingstrong aqueous alkali or acid to remove any residual acidic or basicmaterials which may be present in the organic phase.

The resulting organic fraction may now be processed according toconventional techniques. The organic fraction may be fractionallydistilled, hydrofined, extracted, or the like.

The resulting organic fraction provides a high yield of aromatichydrocarbons, particularly aralkanes in the C -C range. Efficientconversion of the carbonaceous material is achieved with minimalformation of undesirable high molecular weight products, such asasphaltenes. Conversions will exceed weight percent of the carbonaceousmaterial charged, usually exceeding weight percent.

To further understand this invention, the drawing will now beconsidered. Into reactor 10 via line 12 is introduced an aqueous slurryof comminuted coal. Simultaneously, via line 14, a mixture ofsupercritical water and hydrogen are introduced into reactor 10. Thereaction mixture is maintained in the reactor for sufficient time toinsure efficient pyrolysis of the coal, the transformation to thedesired hydrocarbon liquid fractions. The reaction mixture is thentransferred to solids separator 16 via line 20, while maintaining theelevated temperatures and pressures. The solids are withdrawn fromsolids separator 16 via line 22 and the supercritical fluid transferredvia line 24 and flashed into condenser 26.

The gaseous effluent, primarily hydrogen, is processed to remove anyadventitious undesirable reactive materials and recycled via line toline 14 to augment the hydrogen combined with the supercritical water.The mixed liquid phases in condenser 26 are transferred via line 32 toliquid separator 34.

After separation of the organic phase from the aqueous phase, theaqueous phase is withdrawn through line 36, and the organic phase passedvia line 40 through. scrubber 42. The organic effluent free of acidicand basic constituents may then be fractionally distilled and thevarious fractions processed in accordance with conventional techniques.

in accordance with this invention, carbonaceous materials are liquefiedto desirable liquid fuel fractions, particularly C Asphaltene and coaltar formation is minimized. By the use of water and hydrogen as the soleagents, separation is easily achieved, and excess hydrogen may berecovered and recycled. High economy and efficiency is obtained in theconsumption of hydrogen.

Although the foregoing invention has been described in some detail byway of illustration and example for purposes of clarity ofunderstanding, it will be obvious that certain changes and modificationsmay be practiced within the scope of the appended claims.

What is claimed is:

l. A method for liquefying bituminous and subbituminous coal to providehigh yields of C liquid fuel fractions which comprises:

contacting for a period of 1 to 5 minutes in a reaction zone a chargeconsisting of comminuted coal as a relatively cool flowable aqueousslurry, supercritical water, and hydrogen, wherein said water is at atemperature sufficient to maintain a temperature in the reaction zone inthe range of 380 to 650C, and the pressure in the reaction zone ismaintained in the range of about 230 to 700 atm., whereby said coal israpidly raised to the temperature of the reaction zone, and wherein theweight ratio of total water to coal in the reaction zone is in the rangeof from about 1 to 10:1, and the amount of water in said slurry is lessthan about one-half of the total amount of water introduced into saidreaction zone;

separating said effluent into a solid phase and a supercritical fluidphase while substantially maintaining the temperaturesand pressures ofsaid reaction zone,

condensing said supercritical fluid phase into an organic phase enrichedin C-,+ hydrocarbons and an aqueous phase; and

recovering said organic phase.

2. A method according to claim 1, wherein said hydrogen is present infrom about 1 to 10 weight percent based on coal.

3. A method according to claim 2., including the steps of flashing saidsupercritical fluid phase prior to condensing to obtain a gaseous phaseof gaseous hydrocan bons and hydrogen; and

recovering said gaseous phase.

4. A method according to claim 1, wherein the weight ratio of totalwater to coal inthe reactor is from about 1 to 5 parts by weight perpart of coal and the amount of water in said aqueous slurry is fromabout 0.4 to 0.6 parts by weight per part of coal.

5. A method according to claim 1 wherein said temperature is in therange of about 400 to 500C, said pressure is in the range of about 245to 350 atm., the total amount of water is in the range of from about 1to 2 parts by weight per part of coal, and the hydrogen is present infrom 1 to 4 weight percent based on coal.

1. A METHOD FOR LIQUEFYING BITUMINOUS AND SUBBITUMINOUS COAL TO PROVIDEHIGH YIELDS OF C7+ LIQUID FUEL FRACTIONS WHICH COMPRISES, CONTACTING FORA PERIOD OF 1 TO 5 MINUTES IN A REACTION ZONE A CHARGE CONSISTING OFCOMMINUTED COAL AS A RELATIVELY COOL FLOWABLE AQUEOUS SLURRY,SUPERCITICAL WATER, AND HYDROGEN, WHEREIN SAID WATER IS AT A TEMPERATURESUFFICIENT TO MAINTAIN A TEMPERATURE IN THE REACTION ZONE IN THE RANGEOF 380* TO 650*C, AND THE PRESSURE IN STHE REACTION ZONE IS MAINTAINEDIN THE RANGE OF ABOUT 230 TO 700 ATM., WHEREBY SAID COAL IS RAPIDLYRAISED TO THE TEMPERATURE OF THE REACTION ZONE, AND WHEREIN THE WEIGHTRATIO OF TOTAL WATER TO COAL IN THE REACTION ZONE IS IN THE RANGE OFFROM ABOUT 1 TO 10.1, AND THE AMOUNT OF WATER IN SAID SLURRY IS LESSTHAN ABOUT ONE-HALF OF THE TOTAL AMOUNT OF WATER INTRODUCED INTO SAIDREACTION ZONE, SEPARATING SAID EFFULENT INTO A SOLID PHASE AND ASUPERCRITICAL FLUID PHASE WHILE SUBSTANTIALLY MAINTAINING THETEMPERATURES AND PRESSURES OF SAID REACTION ZONE; CONDENSING SAIDSEPERCRITICAL FLUID PHASE INTO AN ORGANIC PHASE ENRICHED IN C7+HYDROCARBON AND AN AQUEOUS PHASE; AND RECOVERING SAID ORGANIC PHASE. 2.A method according to claim 1, wherein said hydrogen is present in fromabout 1 to 10 weight percent based on coal.
 3. A method according toclaim 2, including the steps of flashing said supercritical fluid phaseprior to condensing to obtain a gaseous phase of gaseous hydrocarbonsand hydrogen; and recovering said gaseous phase.
 4. A method accordingto claim 1, wherein the weight ratio of total water to coal in thereactor is from about 1 to 5 parts by weight per part of coal and theamount of water in said aqueous slurry is from about 0.4 to 0.6 parts byweight per part of coal.
 5. A method according to claim 1 wherein saidtemperature is in the range of about 400* to 500*C, said pressure is inthe range of about 245 to 350 atm., the total amount of water is in therange of from about 1 to 2 parts by weight per part of coal, and thehydrogen is present in from 1 to 4 weight percent based on coal.